foo.cc: In function 'bool check(int)':
foo.cc:18:34: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   if (((s >> i) & 1) && ((s >> i + 1) & 1))
                                ~~^~~
foo.cc: In function 'int main()':
foo.cc:43:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < state.size(); ++ i)
                  ~~^~~~~~~~~~~~~~
foo.cc:44:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = 0; j < state.size(); ++ j)
                   ~~^~~~~~~~~~~~~~
foo.cc:54:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int a = 0; a < state.size(); ++ a)
                    ~~^~~~~~~~~~~~~~

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